Silver protective agents for sulfurcontaining lubricants



Patented Oct. 5, 1954 S I LVER PROTECTIVE AGENTS FOR SULFUR- CONTAINING LUBRICANTS Warren Lowe and James 0. Clayton, Berkeley, Calif., assignors to California Research Corporation, San Francisco, Calif., a corporation of Delaware No Drawing. Application October 31, 1950, Serial No. 193,278

1 a The present invention relates to lubricating oils compounded with active sulfur-containing compounds, such as metal salts or thiophosphates,

which composite oils are severely corrosive to silver and like bearings, and to the prevention of such sulfur attack on silver by incorporating in said severely corrosive compounded oils a thiadiazolyl dithiocarbamate, such as 1,3,4-thiadiazolyl-2,5-bis(dialky1 dithiocarbamate) As is well known, the present-day problems involved in the lubrication of internal combustion engines are extremely complex and difficult to overcome, due mainly to the great loads imposed on bearings, the high engine speeds, and the elevated operating temperatures. To avoid rapid deterioration resulting from such severe operating conditions, lubricating oils have been compounded with various improving or stabilizing agents.

Of the various lubricating oil compounding agents, many of the most effective are compounds containing sulfur. For example, aliphatic polysulfides, metal salts of .organo-thiophosphates, etc., are highly effective oxidation inhibitors; and sulfurized olefins, xanthate esters and the like are excellent extreme pressure agents. Unfortunately, oils compounded with such active sulfur-containing compounds are severely corrosive to silver and like metals. The deleterious action involves a direct attack of the metal by sulfur, resulting in a rapid darkening of the metal surface and formation of sulfides and the subsequent sloughing ofi of the sulfides during engine operation. Thus, there is a considerable loss of bearing metal and a pitting of bearing surfaces. This sulfur attack may be designated as sulfur corrosion, as distinguished from corrosion caused by action of acids and peroxides which are found as products of oxidation of lubricating oils, particularly highly-refined lubricating oils. This latter type of corrosion, which may be called "oxidation corrosion, or acid corrosion, adversely affects such hard metal alloys as cadmium-silver, copper-lead, etc., but does not seriously affect silver or bronze. Such oxidation corrosion is usually minimized by the presence of oxidation inhibitors, which reduce the formation of the corrosive acids and peroxides.

It is apparent that in spite of the long desire to lubricate silver bearings with lubricants compounded with active sulfur compounds, it has been impractical to do so in view of the aforementioned severe corrosivity to silver.

Therefore, it is an object of this invention to provide a non-silver-corros-ive lubricant containing active sulfur compounds.

11 Claims. (Cl. 252-47) In the attainment of this object, the present invention concerns a lubricant compounded with active sulfur compounds, which compounded lubricant is severely corrosive to silver, and silverprotective agents which greatly minimize attack on silver by sulfur in the compounded lubricant but without adversely afiecting'the desired func tioning of the sulfur compounds.

Heretofore, in the lubrication of engines having silver metal wearing surfaces, for example, in certain railroad diesel engines which use silver wrist pin bushings, it has been difiicult to prevent sulfur attack of the silver surfaces. Because the silver surfaces (e. g., the silver wrist pin bush-' ings) are susceptible toattack by the sulfur of the sulfur-containing lubricating oil additives, there ha been a tendency to eliminate highly effective sulfur-containing additives from the diesel lubricating oils, thereby losing the remarkable benefits of these additives. As noted hereinabove, certain highly effective lubricating oil antioxidants contain sulfur, which is corrosive to silver. These effective antioxidants have not been used in diesel engines containing silver wrist pin bushings without sulfur attack of the silver. Alternative practices have been to eliminate the sulfur-containing additives from the oil, allowing the oil to deteriorate more rapidly through oxidation; or the sulfur-containing additives have been included in the oil formulation, with the resulting sulfur corrosion of the silver wrist pin bushings. Silver is also used in'wearing surfaces in aircraft engines, but because of the presence of the silver, the highly effective sulfur-containing aviation oil additives are not used. Now, however, by using the compounds of this invention, lubricating oils compounded with sulfurcontaining additives can be used in diesel oils,

aviation oils, and any other oils where sulfur corrosion of metals is a problem.

It is of extreme advantage to use a lubricant composition which is effective not only in inhibiting oxidation corrosion, but which is also effective in preventing sulfur attack on metals. In railroad oils, for example, it has been a handicap to. use lubricants which inhibit corrosion resulting from oxidation products but permit unhampered attack on metals by compounds having active sulfur present.

While the outstanding advantages of the silver protective agents in otherwise severely corrosive lubricants containing sulfur compounds is particularly apparent in heavy duty motor oils, the inventive combination finds application in turgears, cutting oils, soluble oils, greases, etc.

The action of the silver protective agents cannot be explained on any simple basis, since their apparent effect appears anomalous: On the one hand, the protective. agents prevent destructive attack of the sensitive metal by active sulfur compounds; but on the other hand, they do not interfere with the functioning of extreme pressure agents which are believed to act by reaction with the metal surface.

The silver protective agents of this invention which reduce the sulfur attack on silver are thiadiazolyl dithiocarbamates represented by the following formulas:

wherein the Rs represent straight-chained or branch-chained, saturated or unsaturated substantially hydrocarbon (hydrocarbonaceous) radicals selected from the group of alkyl, aralkyl and alkaryl radicals. The alkyl groups present as such or attached to a ring structure each contain from 1 to 20 or more carbon atoms, preferably 2. to 8 carbon atoms. The R groups may or may not be identical.

Examples of the R. groups include ethyl, propyl, propenyl, butyl, butenyl, octyl, octenyl, octadecyl, benzyl, phenyl butyl, phenyl octyl, ethyl phenyl, butyl phenyl, octyl phenyl, etc.

By essentially hydrocarbon (hydrocarbonaceous) .radical is meant those radicals which are composed mainly of hydrogen and carbon, and includes such radicals which contain, in addition, minor amounts of substituents such as chlorine, bromine, oxygen, hydroxyl groups, etc.

Examples of thiadiazolyl dithiocarbamates of this invention include: 1,3,4-thiadiazolyl-2,5- bis(diethyl dithiocarbainate); 1,3,4-thiadiazolyl- 2,5-bis(dibutyl dithiocarbamate); 1,3, l-thiadiazolyl-2,5-bis(dioctyl dithiocarbamate) 1,3,4-thiadiazolyl-2,5 bis(dioctadecyl dithiocarbamate); 1,3,4 thiadiazolyl 2 thiol 5 diethyl dithiocarbamate; l,3,4-thiadiazolyl-2-thiol-5-dibutyl dithiocarbamate; 1,3,4 thiadiazolyl z-thiol- 5-dioctyl dithiocarbamate, etc.

The thiadiazolyl dithiocarbamates of this invention are eilective in inhibiting sulfur corrosion when used in amounts as low as about 0.001% (by weight of total composition). Certain of these compounds have only limited solubility in the lubricating oil and are effective at that solubility. When the thiadiazolyl derivatives have sufficient solubility, they are effective when used in amounts as great as 10.0%. However, it is preferred that the compounds of this invention be used in amounts suffi'cient substantially to reduce the corrosion of silver. For example, it is preferred to use the thiadiazolyl compounds in amounts of from about 0.05 to about 0.50%. The major portion of the lubricating composition of this invention is the base oil.

Suitable base oils include a wide variety of lubricating oils such as naphthenic base, paraffin base, and mixed base mineral oils, other hydrocarbon lubricants, e. g., lubricating oil derived from coal products, and synthetic oils, e. g., alkylene polymers (such as polymers of ing therein thiadiazolyl compounds.

propylene, butylene, etc., and mixtures thereof), alkylene oxide-type polymers, dicarboxylic acid esters and liquid esters of acids of phosphorus. Synthetic oils of the alkylene oxide-type polymer which may be used include those exemplified by the alkylene oxide polymers (e. g., propylene oxide polymers) and derivatives, including alkylene oxide polymers prepared by polymerizing alkylene oxides, e. g., propylene oxide, in the presence of water or alcohols, e. g., ethyl alcohol, and esters of alkylene oxide-type polymers, e. g., acetylated propylene oxide polymers prepared by acetylating propylene oxide polymers containing hydroxyl groups.

Synthetic oils of the dicarboxylic acid ester type include those which are prepared by esterifying such dicarboxylic acids as adipic acid, azelai acid, suberic acid, sebacic acid, alkenyl succinic acid, fumaric acid, maleic acid, etc., with alcohols such as butyl alcohol, hexyl alcohol, Z-ethyl-hexyl alcohol, dodecyl alcohol, etc. Examples of dicarboxylic acid ester synthetic oils include di-butyl adipate, di-hexyl adipate, di-2- ethyl-hexyl sebacate, di-n-hexyl fumarate polymer, etc.

Synthetic oils of the type of liquid esters of acids of phosphorus include the esters of phosphoric acid, e. g., tricresyl phosphate; the esters of phosphonic acid, e. g., di-ethyl ester of decane phosphonic acid (or other such esters as obtained by reacting alkyl phosphonyl chlorides with hydroxyl-containing compounds such as phenols and aliphatic alcohols), and with olefin oxides such as propylene oxide, as described in Jensen et al., U. S. patent application No. 86,856.

The improved lubricant of the present invention is used wherever elemental sulfur or sulfur compounds containing active sulfur attack metals and are severely corrosive to metals which are being lubricated. Thus, as a result of the present invention, lubricants which normally are severely corrosive to metal parts due to attack by sulfur or active sulfur compounds may now be used without fear of corrosion by incorporat- Severely corrosive is defined as that corrosion which causes a weight loss greater than 30 milligrams in the silver strip test noted hereinbelow.

In order to evaluate the agents of this invention for inhibiting corrosion due to active sulfur, a silver strip corrosion test was made on numerous agents of this invention. lhis silver strip corrosion test was performed as follows:

A silver metal strip having the dimensions 01- 2 inches by inch by inch was first cleaned with a wire brush until the strip was highly polished. The strip was weighed and the weight recorded. This highly polished silver strip was then placed in a 600 milliliter beaker in such a manner that the strip was completely immersed when 300 grams of the oil being tested was poured into the beaker. The oil was stirred at a temperature of 300 F. for 20 hours, at which time the silver strip was removed and cleaned,-

first with chloroform, then with petroleum ether. The appearance of the strip was noted. Those strips which had been severely attacked were quite black. The tested silver strip was washed in 15% aqueous solution of potassium cyanide for about 5 minutes to remove the sulfide filmv adhering to the strip. After the strip had been washed with potassium cyanide and dried, it was weighed. The diiference in weight of the original strip and the strip after the potassium cyanide I wash was notedand recorded as the weightloss due to corrosion by the sulfur compound.

-The 1,3,ethiadiazolyl-lB-bis(dialkyl dithiocarbamates) used in-obtaining the data set forth hereinbelow are manufactured by the Sharples Chemical Co., Philadelphia,gPa..

Table I below presents data obtained in the silver strip test and shows the remarkable effects of ,thiadiazolyl dithiocarbamates as silverprotective agents in reducing the attack on silver by a California solvent-defined S. A. E. 30 paraffinic base 011 containing sulfurized calcium cetyl plienate,v sulfurized diparaffin sulfide, calcium petroleum sulfonate and zinc cetyl phenyl dithiophosphate and 1,3,4 thiadiazolyl 2,5 bis- (diethyl dithiocarbamate) Table I OI ir 18 1820 Y Silver Strip 2,5-Bis(Diethl7 p aluoe r gr l sys l ma e in u rieating on (Pep Milli cent by Weig Table Hpr esents, data obtained in the silver strip test ofa solvent-refined S. A E. 30 paraffinic base oil to which was added sulfurized diparaffin sulfide and 1,3,4-thiadiazolyl-2,5-bis- Table III presents data obtained in the silver strip test of a California solvent-refined S. A. E. 30 parafiinic base oil to which was added a dialkyl phenol disulfide, a basic lead petroluem sulfonate and 1,3,4-thiadiazolyl-2,5-bis(diethyl dithiocarbamate.

Table III Amount of 1,3, I 4-'lhiadiazolyl-1 %llVe1"NSt rip Dialkyl Disulflde Used ii g figjgf s S ti mate) (Percent Milligrams by Weight) 1. Diamyl phenol 83. 4 2. Diamyl phenol 0. l 2.3 3. Dioctyl nhennl 136. 6 4. Dioctyl phenol 0. 1 3.7 5. Para-tert-butyl phenol 134.6 6. Para-tert-butyl phenol 0. 1 1. 6

Table IV presents data obtained when the California solvent-refined S. A. E. 30 parafiinic base oil contained a sulfurized diparafiin sulfide, a basic lead petroleum sulfonate and 1,3,4-thiadiazolyl 2,5-bis(diethyl dithiocarbamate).

' Table V presents'data obtained when the California solvent-refined S. A. E. 30 parafli'nic' base oil contained a zinc di-(sec. butyl) dithiophosphate', and a 1,3,4-thiadiazolyl-2,5-bis(dialkyl dithi'ocarbamate) Table 'V Amount of 1,3 Amount of 1,3, 4-Thiadiazolyl 4-Thiadiazolylgggfi i a 2,5-Bis(Diethyl 2,5-BiS(Dibutyl Lossig Dithiocarba- Dithiocarba- Mini rams mate) mate) 3 The agents of this invention are especially effective as protective agents for silver. However, the protective agents of this invention are also efiective in protecting other sulfur-sensitive metals from sulfur attack. Such other sulfursensitive metals include copper, aluminum, and alloys of copper and aluminum.

As illustrative of various sulfur-containing extreme pressure agents, detergents, oxidation inhibitors, etc., which cause oils containing them to be severely corrosive to silver, the following may be mentioned: sulfurized lubricating oils, xanthate esters, chlorinated 'xanthate esters, dialkyldisulfides, sulfurized fatty oils, metal salts of reaction products of olefins and phosphorus pentasulfide, organic trisulfides, tetrasulfides and pentasulfides (e. g., parafiin wax polysulfide), polyvalent metal salts of organo-substituted acids of phosphorus (e. g., zinc hexyldithiophosphate), sulfurized olefins (e. g., sulfurized terpene), xanthic acid derivatives (e. g., dibutyl xanthogen disulfide) etc.

Some of the above-indicated additives are more vigorous in their attack on silver than others, and. consequently such attack is more difficult to minimize. However, the silver-protective agents are advantageously used even with the more active sulfur additives.

The silver-protective agents of this invention are also effective in reducing attack on silver by the sulfur in lubricating oils derived from some of the crude oils characterized by their high sulfur content.

Although the silver protective agents are especially desirable and preferably used in combination with lubricating oils containing the polyvalent metal salts of organo-substituted thioacids of phosphorus (e. g., zinc cetyl phenyl dithiophosphate), they may be used in lubricating oils also containing such compounds as phenates (e. g., calcium cetyl phenate), sulfonates (e. g., calcium petroleum sulfonate), phosphate (e. g., calcium cetyl phosphate), phenols (e. g., 2,6-ditertiary-butyl-l-methyl phenol), phosphonates (e. g., calcium white oil phosphonate), thiophosphenates (e. g., calcium cetyl thiophosphonate), etc.

The silver-protective agents of this invention may be added to lubricating compositions containing other agents than sulfur-active agents, that is, other agents which are advantageously present as oiliness agents, blooming agents, viscosity index improvers, pour point depressants, peptizing agents, thickening agents for greases, etc.

The thiadiazolyl dithiocarbamates of this invention are also efiective in reducing corrosion of silver due to selenium compounds. That is, lubricants which contain active selenium compounds as additives, for example, dialkyl monoselenides, dialkyl diselenides, dialkyl polyselenides, selenomercaptans, metal alkyl selenides, etc., show attack on silver by selenium. However, the protective agents of this invention inhibit the attack on silver by lubricants containing selenium compounds.

We claim:

1. A lubricant consisting essentially of a major portion of a sulfur-containing lubricating oil composition severely corrosive to silver, and a small amount, sufilcient substantially to reduce the sulfur attack on silver, of a 1,3,4-thiadiazolyl- 2,5-Fbis(dialkyl dithiocarbamate) said alkyl radical containing from 1 to 20 carbon atoms.

2. A lubricant consisting essentially of a major portion of a sulfur-containing lubricating oil composition which is severely corrosive to silver, and added to said sulfur-containing lubricating oil composition, a 1,3,4-thiadiazoly1-2,5-bis(dialkyl dithiocarbamate), said alkyl radical containing from 2 to 8 carbon atoms.

3. A lubricating oil composition, at least 95% of which is composed of an admixture of an oil of lubricating viscosity and lubricating oil additives having present sulfur, which admixture is corrosive to silver, and compounded with .this mixture a 1,3,4-thiadiazolyl-2,5-bis(dialkyl dithiocarbamate), said alkyl radical containing from 2 to 8 carbon atoms.

4. A lubricant consisting essentially of a major portion of a sulfur-containing lubricating oil composition severely corrosive to silver, and a small amount, sufficient substantially to reduce the sulfur attack on silver, of a 1,3,4-thiadiazolyl-2-5- bis(dialkyl dithiocarbamate), said alkyl radical containing from 2 to 8 carbon atoms.

5. A lubricant consisting essentially of a. major portion of a sulfur-containing lubricating oil composition severely corrosive to silver, and a small amount, suflicient substantially to reduce the sulfur attack on silver, of 1,3,4-thiadiazolyl- 2-5-bis(diethyl dithiocarbamate) 6. A lubricant consisting essentially of a major portion of a sulfur-containing lubricating oil composition severely corrosive to silver, and a small amount, sufficient substantially to reduce the sulfur attack on silver, of 1,3,4-thiadiazolyl- 2-5-bis(dibutyl dithiocarbamate) 7. A lubricating oil composition at least of which is composed of an admixture of an oil of lubricating viscosity and lubricating oil additives having present sulfur, which admixture is corrosive to silver, and compounded with this mixture from 0.1 to 5.0% of 1,3,4-thiadiazolyl- 2-5-bis (diethyl dithiocarbamate) 8. A lubricating oil composition at least 95% of which is composed of an admixture of an oil of lubricating viscosity and lubricating oil additives having present sulfur, which admixture is corrosive to silver, and compounded with this mixture from 0.1 to 5.0% of 1,3,4-thiadiazolyl- 2-5-bis(di-butyl dithiocarbamate) 9. A sulfur-containing lubricant severely cor-- rosive to silver and a small amount suflicient sub-. stantially to reduce the sulfur attack on silver of a 1,3,4-thiadiazolyl-2-5-bis(dialkyl dithiocarbamate), said alkyl radical containing from 2 to 8 carbon atoms.

10. A sulfur-containing lubricant severely corrosive to silver and a small amount sufficient substantially to reduce the sulfur attack on silver of a 1,3,4-thiadiazolyl-2-5-bis(diethyl dithiocarbamate).

11. A sulfur-containing lubricant severely corrosive to silver and a small amount sufficient substantially to reduce the sulfur attack on silver of a 1,3,4-thiadiazolyl-2-5- bis(dibutyl dithiocarbamate) References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,285,410 Bousquet et a1 June 9, 1942 2,343,393 Bergen Mar. 7, 1944 2,366,539 McCleary Jan. 2, 1945 2,371,319 Ross et al Mar. 13, 1945 

1. A LUBRICANT CONSISTING ESSENTIALLY OF A MAJOR PORTION OF A SULFUR-CONTAINING LUBRICATING OIL COMPOSITION SEVERELY CORROSIVE TO SILVER, AND A SMALL AMOUNT, SUFFICIENT SUBSTANTIALLY TO REDUCE THE SULFUR ATTACK ON SILVER, OF A 1,3,4-THIADIAZOLYL2,5-BIS(DIALKYL DITHIOCARBAMATE), SAID ALKYL RADICAL CONTAINING FROM 1 TO 20 CARBON ATOMS. 